Re: [RFC PATCH v8 00/16] Provide a zero-copy method on KVMvirtio-net.

From: Shirley Ma
Date: Fri Jul 30 2010 - 11:49:54 EST

Hello Avi,

On Fri, 2010-07-30 at 08:02 +0300, Avi Kivity wrote:
> get_user_pages() is indeed slow. But what about
> get_user_pages_fast()?
> Note that when the page is first touched, get_user_pages_fast() falls
> back to get_user_pages(), so the latency needs to be measured after
> quite a bit of warm-up.

Yes, I used get_user_pages_fast, however if falled back to
get_user_pages() when the apps doesn't allocate buffer on the same page.
If I run a single ping, the RTT is extremely high, but when running
multiple pings, the RTT time reduce significantly, but still it is not
as fast as copy from my initial test. I am thinking that we might need
to pre-pin memory pool.


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